Thanks ReDSanchous for the reply.
девушка and девочка have different meanings. One is for a small girl. The other one is for a grown up girl.

For me, it is difficult to distinguish between the two.I guess for a grown up girl it should be девушка.

Please tell me if I am wrong.

Yes, девушка. You may call her девочка but that word usually bears either a very intimate (when addressing her directly in private) or a scornful meaning.
Девочки referring to a grown up girls may be used also to refer to a group of prostitutes.